Hydraulic power transmission systems



April 16, 1963 H. J. HAMBLIN ETAL 3,085,403

, HYDRAULIC POWER TRANSMIHSSION SYSTEMS Filed July 5, 1961 United States Patent HYDRAULIC POWER TRANSMISSION SYSTEMS Henry Joel Hamblin, Putnoe, and Harry James Nation,

Silsoe, England, assignors to National Research Development Corporation, London, England, a British corporation Filed July 5, 1961, Ser. No. 121,986 3 Claims. (Cl. 6tl97) This invention relates to hydraulic power transmission systems of the kind in which a plurality of hydraulic motors receive their motive fluid from a common supply.

It is an object of the invention to prevent substantial loss of power 'fDOlTl the remaining motor or motors in the event of a reduction of load on one or more of the motors. In the event of a reduction of load on a motor it would begin to overspeed and receive additional motive fluid at the expense of the remaining motor or motors. In the extreme case the lightly loaded motor would run away and the remaining motors would stop.

According to the present invention, in a hydraulic power transmission system having a plurality of hydraulic motors which receive their motive fluid from a common supply there is associated with each motor an auxiliary pump driven at a speed dependent upon the speed of the motor, the auxiliary pumps are connected in a circuit, the delivery of one auxiliary pump feeding the inlet of the next and so on, and the delivery side of each auxiliary pump is connected to a pressure-sensitive actuating member for a throttle valve in the motive fluid supply line to the respective motor.

Thus in the event of a motor overspeeding, the auxiliary pump driven by this motor will deliver more fluid than the following auxiliary pump can take and consequently the pressure between these pumps will rise. This rise in pressure will act on the throttle valve of the overspeeding mot-or whereby its supply of motive fluid will be throttled and its speed will be correspondingly reduced. Each auxiliary pump may be driven, for example, by means such as an auxiliary hydraulic motor which rotates at a speed dependent upon the rate of flow of mo tive fluid to or from the respective main motor, but preferably each auxiliary pump is mechanically driven directly or indirectly by its respective motor.

If the capacity of the circuit is insufficient, the lines connecting the auxiliary pumps may be connected to a reservoir :or other supply of hydraulic fluid through nonreturn valves. In the event of an auxiliary pump overspeeding this pump will draw in additional fluid through the non-return valve on its upstream side, the amount so drawn in being substantially equal to the amount required to actuate the throttle valve of the overspeeding motor which is connected to the delivery side of this pump. If local pressure is insufficient to ensure opening of the non-return valves, intake of fluid to the auxiliary pump circuit can be guaranteed by subjecting all the non-return valves to a supply of fluid under moderate pressure, for instance the base pressure of the motive fluid in the transmission system.

In a fully reversible system provision may be made for reversing the connections between the auxiliary pump circuit and the throttle valve actuating members so that what in the forward regime was the inlet side of each pump and is the delivery side in the reverse regime, is in the latter regime connected to the throttle valve actuating member of the respective motor. Alternatively, if conditions in reverse regime are such thatno provision against overspeeding is necessary, the supply of motive fluid to the throttle valve actuating members can simply be cut off inthis regime.

The invention may be performed in various ways, and

Patented Apr. 16, 1963 "ice one specific embodiment applied to an agricultural tractor will now be described by way of example with reference to the accompanying drawing, which is a diagram of the power transmission system.

Referring to the drawing, the tractor engine (not shown) drives a variable delivery positive displacement hydraulic pump '1. The pump delivers oil into a passage 2 of a throttle valve assembly 3, and the oil then flows through two throttling orifices 4 and 5 to two hydraulic motors 6 and 7 mounted respectively in the two rear wheels of the tractor. Oil discharged from these motors returns to the throttle valve assembly 3 wherein it passes through two throttling orfices 8 and 9 and returns through a passage 10 to the inlet side of the pump 1.

Rigidly attached to the motors 6 and 7 are gears 11 and 12 respectively, these gears driving auxiliary hydraulic pumps 13 and 14. These pumps preferably have a pulse-less delivery characteristic to avoid risk of hunting at low speed due to phase differences between the two pumps. The discharge side of each auxiliary pump is connected to the inlet side of the other auxiliary pump by lines 15 and 16, forming a continuous circuit.

The lines 15 and 16 are respectively connected to annular ports 17 and 18 in a reversing valve 19. The valve 19 has a shuttle spool 22 which is moved into, and maintained in, one or other of its two end positions by a control member such as a rod 21, this member being interconnected with a reversing control member (not shown) for the pump 1. The arrangement is such that the shuttle spool 22 will occupy one end position during forward motion of the tractor and the other end position during reverse motion.

In one end position of the shuttle spool 22 the an nular port 17 is connected to one end 23 of the throttle valve assembly 3 while the other annular port 18' is connected to the opposite end 24, whereas in the other end position of the shuttle spool these connections are reversed.

The throttle valve assembly includes a throttling spool 25 having four control edges which respectively control the throttle orifices 4, 5, 8 and 9, and the ends of the throttling spool are hollowed out to accommodate springs 26 and 27 which bias the spool towards a central position.

In order to ensure a positive pressure in the circuit of the auxiliary pumps 13 and 14, the lines 15 and 16 are fed by oil at the basic or boost pressure of the hydraulic system through non-return valves 28.

Oil which leaks past the lands of the throttling spool 25 is collected in annular channels 29, 30' and 31 connected to a drain line 32. Leakage oil from the motors 6 and 7 also enters the drain line 32.

In the centre of the throttling spool 25 is a groove which receives a pin 33 mounted eccentrically on a shaft 34. Normally this shaft is freely rotatable so that it does not restrict movements of the throttling spool 25.

In normal operation, with both wheel motors 6 and 7 travelling at the same speed, the auxiliary pumps 13 and 14 will both be running at the same speed and the pressures in the lines 15 and 16 and hence at the ends 23 and 24 of the throttle valve assembly will be equal. Thus the throttling spool 25 will occupy its central position and the orifices 4, 5, 8 and 9 will be of equal size.

Should one wheel motor, for example 6, overspeed for any reason, for instance due to wheel slip, the auxiliary pump 13 will run faster than the pump 14 and deliver more oil than the latter can accept. Pressure will therefore build up in the line 15 and at the left-hand end 23 of the throttling spool 25. The throttling spool will therefore move to the right, restricting the orifices 4 and 8. This has the eifect of reducing the flow of oil from the pump 1 to the overspeeding motor 6 and increasing the flow to the rnotor'7.- An equilibrium is reached at a certain permissible excess speed of the motor 6 in relation to that of the motor 7.

Should it be desired to put the anti-slip system out of action, for instance in order not to hinder difierential rotation of the driving wheels-in sharp turns, the shaft 34- is locked with the throttling spool 25 in its central position.

For reverse operation, the delivery of the pump 1 is reversed supplying oil to the passage 10 and receiving oil from thepassage 2. The reversing spool 22 is thereby moved to its left-hand end position so that it reverses theconnections of the lines and 16 to the throttle valve assembly 3. The flow in the circuit of the auxiliary pumps 13 and 14 is also reversed. Therefore, if the motor 6 overspeeds in reverse the pressure in the line 16 will rise, and owing to the reversal of the connections, the throttling spool 25 will again be moved to the right to throttle the flow through this motor.

To facilitate manufacture the throttling spool 25 may be made in two halves, the division being at the central groove which accommodates the eccentric pin 33, since at all times the throttling spool is loaded towards its centre.

In the modification (not illustrated) the throttling spool is servo-actuated, the excess pressure in the auxiliary pump circuit serving to move a control piston which itself controls the admission and discharge of motive fluid to a servo motor which actuates the throttling spool. The

motive fluid for the servomotor is taken from the main pump and motor circuit or the base circuit.

What we claim as our invention and desire to secure by Letters Patent is:

1. A hydraulic power transmission system comprising a plurality of hydraulic motors, motive fluid supply means common to all said hydraulic motors, individual motive fluid supply lines from said common motive fluid supply means to each of said hydraulic motors connecting said hydraulicmotors in parallel, a throttle valve in each said supply line, a pressure-sensitive actuating member for each said throttle valve, a plurality of auxiliary pumps equal in number to said hydraulic motors, a, driving connection from each of said hydraulic motors to a different one of said auxiliary pumps to drive each of said auxiliary pumps at a speed dependent upon the speed of its respective hydraulic motor, each of said auxiliary pumps having a hydraulic fluidinlet and a hydraulic fluid outlet, a plurality of conduit means connecting said auxiliary pumps in a hydraulic circuit With said fluid outlet of one auxiliary pump connected to said fluid inlet of the next auxiliary pump in the circuit and so on around the circuit, each of said conduit means being capable of sustaining internal pressure, and a connection from each of said conduit means to the pressure-sensitive actuating member of the throttle valve in the supply line to the hydraulic motor which drives the auxiliary pump whose outlet is connected to the respective conduit means.

2. A hydraulic power transmission system according to claim 1 in which said driving connections from said hydraulic motors to the respective auxiliary pumps are mechanical driving connections.

3. A hydraulic power transmission system according to claim 1 including individual motive fluid return lines from said hydraulic motors, means for changing over the supply of motive fluid to said return lines for reverse operation of said hydraulic motors and said auxiliary pumps and means for simultaneously establishing a connection to the pressure-sensitive actuating member of the throttle valve associated with each hydraulic motor from the conduit means connected to what, in forward operation, is said inlet of the respective auxiliary pump but which, in reverse operation, is the outlet of said auxiliary pump.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A HYDRAULIC POWER TRANSMISSION SYSTEM COMPRISING A PLURALITY OF HYDRAULIC MOTORS, MOTIVE FLUID SUPPLY MEANS COMMON TO ALL SAID HYDRAULIC MOTORS, INDIVIDUAL MOTIVE FLUID SUPPLY LINES FROM SAID COMMON MOTIVE FLUID SUPPLY MEANS TO EACH OF SAID HYDRAULIC MOTORS CONNECTING SAID HYDRAULIC MOTORS IN PARALLEL, A THROTTLE VALVE IN EACH SAID SUPPLY LINE, A PRESSURE-SENSITIVE ACTUATING MEMBER FOR EACH SAID THROTTLE VALVE, A PLURALITY OF AUXILIARY PUMPS EQUAL IN NUMBER TO SAID HYDRAULIC MOTORS, A DRIVING CONNECTION FROM EACH OF SAID HYDRAULIC MOTORS TO A DIFFERENT ONE OF SAID AUXILIARY PUMPS TO DRIVE EACH OF SAID AUXILIARY PUMPS AT A SPEED DEPENDENT UPON THE SPEED OF ITS RESPECTIVE HYDRAULIC MOTOR, EACH OF SAID AUXILIARY PUMPS HAVING A HYDRAULIC FLUID INLET AND A HYDRAULIC FLUID OUTLET, A PLURALITY OF CONDUIT MEANS CONNECTING SAID AUXILIARY PUMPS IN A HYDRAULIC CIRCUIT WITH SAID FLUID OUTLET OF ONE AUXILIARY PUMP CONNECTED TO SAID FLUID INLET OF THE NEXT AUXILIARY PUMP IN THE CIRCUIT AND SO ON AROUND THE CIRCUIT, EACH OF SAID CONDUIT MEANS BEING CAPABLE OF SUSTAINING INTERNAL PRESSURE, AND A CONNECTION FROM EACH OF SAID CONDUIT MEANS TO THE PRESSURE-SENSITIVE ACTUATING MEMBER OF THE THROTTLE VALVE IN THE SUPPLY LINE TO THE HYDRAULIC MOTOR WHICH DRIVES THE AUXILIARY PUMP WHOSE OUTLET IS CONNECTED TO THE RESPECTIVE CONDUIT MEANS. 